Water purification for drinking and industrial use is critical to the functioning of our modern economy. One of the common methods used to filter water is reverse osmosis. Osmosis is the process by which pure water passes through a semipermeable membrane into aqueous solution (water with a dissolved substance) on the other side of the membrane. Osmotic pressure is the pressure exerted in forcing the pure water through the semipermeable membrane and into the aqueous solution. Reverse osmosis is the process of apply pressure greater than the osmotic pressure on the aqueous solution side of the semipermeable membrane. This forces the water through the semipermeable membrane that screens the dissolved substances in the aqueous solution. The problem with reverse osmosis is it inefficient. The process is very slow in producing purified water. In addition, the semipermeable membranes have to be replaced periodically, which adds to the expense associated with reverse osmosis.
Ion exchange, another common water purification technique, takes advantage of the fact that most impurities in water dissociate into ions. Ion exchangers contain cationic resins and anionic resins. The cationic resins consist of polymer beads charged with hydrogen ions. When water passes through the cationic resins the positively charged ions in the water are exchanged for the hydrogen ions. The water then passes through anionic resins that exchange hydroxide ions for the negatively charged ions. The hydrogen ions and the hydroxide ions combine to form water, thus eliminating the impurities in the water. Eventually, the resins become used up and need to be either replaced or regenerated. Both processes are expensive.
Thus, there exists a need for a method and apparatus that efficiently removes impurities from water and in which the filtration elements can be replaced or regenerated inexpensively.